Problem with my 2002 Tacoma 4cyl. please help!!!!!!!!!!

I have a 2002 Tacoma 2wd reg cab with a 2.4L 4cyl. One day while
driving I came to a stop when all of the sudden the engine stumbled
then stalled on me. When I tried to start it again it would just run
for a second then stall. I had to keep my foot on the gas to keep it
from stalling again. After I got the truck home I began to investigate
what went wrong. The check engine light never came on.

When I can get the truck to idle the engine runs really rough and I can
see black smoke coming out of the exhaust telling me its running very
rich. I changed the sparkplugs and checked the compression of the
engine and its within spec. I also changed out the coils packs that
connects to each spark plug. At this point I assumed it was the MAF
sensor so I replaced it but the problem still remains. I also replaced
the air/fuel & rear oxygen sensors but that didn't seem to help.

I hooked up an OBD2 scan tool to monitor the various sensors while the
truck is idling and noticed the ecu is retarding timing which I'm
assuming is causing the engine to run rich & rough idle. The check
engine light never came on so I don't know why the ECU is pulling back
timing.I notice when I unplug the MAF sensor the truck runs normal. I'm
guessing the ECU is running in "limp mode" at this point but when I
reconnect the MAF sensor the problem comes back. Eveything is telling
me the problem lies with the MAF sensor but I've replaced it with a
brand new one. I even tested out the old MAF sensor on a friends Tacoma
and it runs fine.

Does anybody have any ideas to what the problem could be? I'm at a
loss................

Did you verify in the data list that the coolant temp sensor is telling
the computer the proper temperature? Usually when they go bad they report
absurdly low temps (-44F), causing the ECU to go back into open loop mode
and richen the crap out of the mixture. This, of course, is not good when
the engine is already warm.

qslim wrote:[color=blue]
> Did you verify in the data list that the coolant temp sensor is telling
> the computer the proper temperature? Usually when they go bad they report
> absurdly low temps (-44F), causing the ECU to go back into open loop mode
> and richen the crap out of the mixture. This, of course, is not good when
> the engine is already warm.[/color]

The coolant temp looked normal. At full operating temp the scan tool
showed between 170-180 deg. I also checked the TPS and it's within
spec. Could the problem be with the knock sensor? Remember the truck
isn't throwing any codes.

Thanks

Here are the results from the scan tool. This is with the truck idling

TPS (%) - 13.3%

RPM - 507

Eng. Load (%) - 100.0%

MAF - 3.71

Coolant Temp (F) - 163F

Intake Air Temp (F) - 66F (same as ambient temp.)

Ignition Timing - -9.5 deg

Long Term Fuel Trim (%) - 0

Short Term Fuel Trim (%) - -20.3

Fuel System Status - Closed

Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 2) (V) - 0

Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 1) (V) - 3.0

Note the Ign. timing is at -9.5 deg. and the MAF sensor voltage is at
3.71. Also note the fuel trims.

Why is the calculated engine load at 100% at idle? Have you tested the
throttle position sensor?

qslim wrote:[color=blue]
> Why is the calculated engine load at 100% at idle? Have you tested the
> throttle position sensor?[/color]

I don't know why it's like that. According to the scan tool the TPS is
within spec.

"gmiyahira" <miyahira@hotmail.com> wrote in message
news:1149709705.402810.132990@i39g2000cwa.googlegroups.com...[color=blue]
>
> qslim wrote:[color=green]
>> Why is the calculated engine load at 100% at idle? Have you tested the
>> throttle position sensor?[/color]
>
> I don't know why it's like that. According to the scan tool the TPS is
> within spec.
>[/color]

100% engine load at idle is not within spec !

Exactly. The fuel management is percieving that the engine is fully loaded
(or requesting full load), and is matching fuel delivery accordingly. Does
that figure change at all during run, or is it always pegged at 100%?
Also, your MAF data line, is your scanner providing that format in
grams/sec?
And when you say the TPS is fine according to the scantool, are you
going by the dataline change compared to your foot on the throttle/ fact
that no codes exist/ or have you checked the TPS with a meter to verify
voltage readings?

qslim wrote:[color=blue]
> Exactly. The fuel management is percieving that the engine is fully loaded
> (or requesting full load), and is matching fuel delivery accordingly. Does
> that figure change at all during run, or is it always pegged at 100%?[/color]


It's usually pegged at 100% when I have the MAF sensor connected. When
I run the truck with the MAF sensor disconnected "limp mode" the load
is around 20% (within spec)
[color=blue]
> Also, your MAF data line, is your scanner providing that format in
> grams/sec?[/color]

I'm not sure about that. I think its just measuring the voltage coming
from the MAF sensor signal wire.I know with the trucking running normal
the voltage is supposed to be like 1.3-1.6v at idle give to take but
now is at 3-4v which is not right. I did replace the MAF sensor so its
not the problem.

[color=blue]
> And when you say the TPS is fine according to the scantool, are you
> going by the dataline change compared to your foot on the throttle/ fact
> that no codes exist/ or have you checked the TPS with a meter to verify
> voltage readings?[/color]

The way I checked the TPS was according to the FSM with the throttle
fully closed it should be between 7-11% and fully opened it should be
between 65-75%. I hooked up the scan tool and while the truck is
running I depress the throttle and check the % by the scan tool. With
the throttle closed it measures 11% and when the throttle is fully
opened it measures 75%.

"gmiyahira" <miyahira@hotmail.com> wrote in message
news:1149490596.632998.231020@j55g2000cwa.googlegroups.com...[color=blue]
>I have a 2002 Tacoma 2wd reg cab with a 2.4L 4cyl. One day while
> driving I came to a stop when all of the sudden the engine stumbled
> then stalled on me. When I tried to start it again it would just run
> for a second then stall. I had to keep my foot on the gas to keep it
> from stalling again. After I got the truck home I began to investigate
> what went wrong. The check engine light never came on.
>
> When I can get the truck to idle the engine runs really rough and I can
> see black smoke coming out of the exhaust telling me its running very
> rich. I changed the sparkplugs and checked the compression of the
> engine and its within spec. I also changed out the coils packs that
> connects to each spark plug. At this point I assumed it was the MAF
> sensor so I replaced it but the problem still remains. I also replaced
> the air/fuel & rear oxygen sensors but that didn't seem to help.
>
> I hooked up an OBD2 scan tool to monitor the various sensors while the
> truck is idling and noticed the ecu is retarding timing which I'm
> assuming is causing the engine to run rich & rough idle. The check
> engine light never came on so I don't know why the ECU is pulling back
> timing.I notice when I unplug the MAF sensor the truck runs normal. I'm
> guessing the ECU is running in "limp mode" at this point but when I
> reconnect the MAF sensor the problem comes back. Eveything is telling
> me the problem lies with the MAF sensor but I've replaced it with a
> brand new one. I even tested out the old MAF sensor on a friends Tacoma
> and it runs fine.
>
> Does anybody have any ideas to what the problem could be? I'm at a
> loss................
>[/color]


We have a late model Ford SUV in the driveway that did a very similar thing.
In our case, it was the MAF sensor. We proved it by creating the same
symptoms by disconnecting the new one while the motor was running. I wish I
could tell you where the wires go, but since you've swapped the MAF with
another, and the "bad" one works in the other car and the good one fails in
your car, then I'd be looking to the wire harness for the problem.

"gmiyahira" <miyahira@hotmail.com> wrote:
[color=blue]
>Here are the results from the scan tool. This is with the truck idling
>
>TPS (%) - 13.3%
>
>RPM - 507
>
>Eng. Load (%) - 100.0%
>
>MAF - 3.71
>
>Coolant Temp (F) - 163F
>
>Intake Air Temp (F) - 66F (same as ambient temp.)
>
>Ignition Timing - -9.5 deg
>
>Long Term Fuel Trim (%) - 0
>
>Short Term Fuel Trim (%) - -20.3
>
>Fuel System Status - Closed
>
>Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 2) (V) - 0
>
>Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 1) (V) - 3.0
>
>Note the Ign. timing is at -9.5 deg. and the MAF sensor voltage is at
>3.71. Also note the fuel trims.
>[/color]
Looks to me that the Bank 1, Sensor 2 02 sensor (or the cable) has gone south.
0V is a absurdly lean reading, so the ECM is trying to compensate by enriching
the mixture.

[color=blue]
> Looks to me that the Bank 1, Sensor 2 02 sensor (or the cable) has gone south.
> 0V is a absurdly lean reading, so the ECM is trying to compensate by enriching
> the mixture.[/color]

I have replaced both the Air/Fuel & O2 sensors and checked the wiring
from the sensor plugs all the way back to the ECU. The problem still
remains.

When the truck idles in limp mode the scan tool shows that both the
Long Term & Short Term fuel trims are at 0. I assume at this point the
ecu isn't reading any feedback from the A/F & O2 sensors. But when I
run the truck with the MAF sensor plugged in the Long Term fuel trim
stays at 0 while the Short Term fuel trim is at -20. I'm guessing thats
why the ECU is pulling back timing and dumping fuel into the engine.
Can someone explain to me what Long Term fuel trim exactly is and what
could cause the Long Term fuel trim to stay at 0 and not change?

The most fustrating part of all this is the ecu is not throwing a CEL
so I don't know where to look for a problem. The only time when the CEL
light comes on is when I disconnect the MAF sensor so the truck would
run on limp mode.

[color=blue]
> We have a late model Ford SUV in the driveway that did a very similar thing.
> In our case, it was the MAF sensor. We proved it by creating the same
> symptoms by disconnecting the new one while the motor was running. I wish I
> could tell you where the wires go, but since you've swapped the MAF with
> another, and the "bad" one works in the other car and the good one fails in
> your car, then I'd be looking to the wire harness for the problem.[/color]

I considered that there might be a short somewhere so what I ended up
doing was remove the entire engine harness from the truck and do a
continuity test from each sensor plug to the ecu harness and every
single wire checked out fine.

"Andy Hill" <andy_hill@hp.com> wrote in message
news:s9eg821nbfh35lll6ikv8dsvj49jvt85to@4ax.com...[color=blue]
> "gmiyahira" <miyahira@hotmail.com> wrote:
>[color=green]
>>Here are the results from the scan tool. This is with the truck idling
>>
>>TPS (%) - 13.3%
>>
>>RPM - 507
>>
>>Eng. Load (%) - 100.0%
>>
>>MAF - 3.71
>>
>>Coolant Temp (F) - 163F
>>
>>Intake Air Temp (F) - 66F (same as ambient temp.)
>>
>>Ignition Timing - -9.5 deg
>>
>>Long Term Fuel Trim (%) - 0
>>
>>Short Term Fuel Trim (%) - -20.3
>>
>>Fuel System Status - Closed
>>
>>Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 2) (V) - 0
>>
>>Heated Exhaust Gas Oxygen Sensor (bank 1, sensor 1) (V) - 3.0
>>
>>Note the Ign. timing is at -9.5 deg. and the MAF sensor voltage is at
>>3.71. Also note the fuel trims.
>>[/color]
> Looks to me that the Bank 1, Sensor 2 02 sensor (or the cable) has gone
> south.
> 0V is a absurdly lean reading, so the ECM is trying to compensate by
> enriching
> the mixture.[/color]


The bank 1, sensor 2 does not affect the fuel mixture. It's only purpose
is to monitor the efficiency of the catalytic converter.

"gmiyahira" <miyahira@hotmail.com> wrote in message
news:1149792859.877762.94490@j55g2000cwa.googlegroups.com...[color=blue]
>[color=green]
>> We have a late model Ford SUV in the driveway that did a very similar
>> thing.
>> In our case, it was the MAF sensor. We proved it by creating the same
>> symptoms by disconnecting the new one while the motor was running. I wish
>> I
>> could tell you where the wires go, but since you've swapped the MAF with
>> another, and the "bad" one works in the other car and the good one fails
>> in
>> your car, then I'd be looking to the wire harness for the problem.[/color]
>
> I considered that there might be a short somewhere so what I ended up
> doing was remove the entire engine harness from the truck and do a
> continuity test from each sensor plug to the ecu harness and every
> single wire checked out fine.[/color]


You need to check the harness while it is installed in the vehicle. You
would be looking for a wire that is shorted to power or ground.